Verified with 'vpython -vpython-spec gsutil.vpython -vpython-tool verify

Bug: 875100
Change-Id: I1efafa0ddc2e2074eba605e8b7f0b69fce124679
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3351475
Auto-Submit: Brian Ryner <bryner@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>